Induction sealing of paperboard

ABSTRACT

A method and apparatus for use in form, fill, and seal machines wherein a polyfoil material is compressed between two jaws, one jaw having a secondary induction coil which passes through an electromagnetic field and induces a current in the metallic layer of the polyfoil, to heat and then seal the polyfoil. In a preferred embodiment, a plurality of nonconductive sealing jaws, each containing a secondary induction coil, are mounted on an endless carrying means and a plurality of opposing corresponding rigid pressure jaws are also mounted on an endless carrying means and are arranged so that, as the carrying means advance continuously, each sealing jaw and corresponding pressure jaw contact and compress together facing thermoplastic layers of a polyfoil material and each secondary coil passes through an electromagnetic field to induce a current in the secondary induction coil which in turn induces a current in the area of the metallic foil layer proximate to the secondary induction coil to heat the foil and soften the adjacent thermoplastic materials which, because they are pressed together, will fuse and harden upon cooling. In continuous transverse sealing of a filled polyfoil tube, the pressure jaws may include a knife to sever the seals, the polyfoil tube may be preformed before it is sealed, and the sealing and pressure jaws may have an alignment means to facilitate severing and sealing. The secondary induction coil is preferably an enlongated twin loop coil folded so that one loop is fully subjected to the electromagnetic field and the second loop induces a current in the polyfoil tube.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for sealingpaperboard packaging material, a laminate including a layer of metallicfoil, an exterior layer of a thermoplastic material, and a layer ofpaper ("polyfoil"). The thermoplastic layer is utilized as the sealant,and the thermoplastic material of one polyfoil area is fused to thethermoplastic material of a second polyfoil area.

Polyfoils having a metallic foil layer such as aluminum foil, anexterior thermoplastic layer such as polyethylene or polypropylene, anda structural paperboard layer have been used advantageously in makingcontainers for food products and liquid products. Polyfoil isimpermeable to liquid, resistant to fatty substances, acids, and thelike, and can be sealed to itself by heating and pressing together twofacing thermoplastic surfaces so that the thermoplastic material softensand fuses together. Upon removing the heat, the thermoplastic materialhardens as one mass, forming a substantially airtight seal, preferably ahermetic seal.

In one commercial practice, a single web of polyfoil paperboard laminateis folded over, heated, and sealed longitudinally to form a tube. Thetube is sterilized before, during or after construction, filled with afluid such as milk or orange juice, and sealed transversely, envelopingthe substance in a hermetically sealed, airtight, sterile package. Theevelope is then severed from the tube being continuously formed above,through the area seaed, resulting in a discrete package having seals atside, top, and bottom, and a seal at the bottom or end of the tube. Thecontainer may then be formed into a parallelepiped or tetrahedal forhandling and shipping.

To achieve the seal, the opposing thermoplastic materials must bepressed together, heated, softened, fused, and allowed to cool beforethe pressure is removed. Several methods of heating the thermoplasticmaterials have been used. One technique is using radiant heat; heatingthe thermoplastic by conduction. Typically heater elements are locatedin the same means that compresses the polyfoil together, for example,resistance welding jaws having Nichrome wire or other resistance elementat the pressure surface or heated pressure belts. E.g., U.S. Pat. Nos.3,940,305 to Stenberg, 3,927,297 and 3,948,720 to Reil, 3,874,976 toMcFarland, Jr., 3,140,218 to Hannon, 2,621,704 to Langer and 2,542,901to Chaffee. Other techniques apply heat radiantly to the plastic, forexample, using a quartz lamp and a heat transmitting pressure diaphramas shown in Abramson et al. U.S. Pat. No. 3,472,721. One furthertechnique is to heat the heating element by induction at one locationand then move the heated element to a second location where it contactsand heats the thermoplastic material by conduction, e.g., Garbini et al.U.S. Pat. No. 3,883,386.

The use of conduction heating is inefficient for sealing polyfoil. Thepaperboard layer acts as an insulator and if the heat is too high thepaper will ignite before the thermoplastic material has fused. Themetallic foil layer acts to dissipate the heat before it reaches thethermoplastic. This results in wasting excessive amounts of energy inheating the paperboard and foil to heat the thermoplastic. Furthermore,some means of cooling the softened thermoplastic while it remains underpressure must often be provided to form an integral seal.

A second technique that has been used with some thermoplastic materialsand heat curable adhesives involves heating ther materialdielectrically; generating an electromagnetic field having a frequencyin a range from about 1 MHz to 2.4 GHz, to induce a dielectric currentin the material directly. These dielectric currents generate heat thatwill soften thermoplastic material and activate thermosetting adhesive.Electromagnetic fields for dielectric heating of thermoplastic orthermosetting materials can be generated between electrically conductingendless belts for heating sheets of synthetic resins, e.g., U.S. Pat.Nos. 4,316,709 to Petersson et al., and 2,492,530 to Kriegsheim; or bypassing the materials to be heated over openings in waveguides, e.g.,U.S. Pat. Nos. 4,060,443 to Balla, 3,109,080 to Pungs et al., and2,506,626 to Zotto. Microwave energy can also be used to cure heatcurable epoxy adhesives, e.g., U.S. Pat. Nos. 4,186,044 to Bradley etal., 4,160,144 to Kayshap et al., 3,707,773 to Wolfberg et al.,3,027,443 to Reed et al., 2,708,649 to Cunningham, 2,631,642 toRichardson et al., 2,612,595 to Warren, 2,479,290 to Auxier et al.

Dielectric heating is not a practicable technique because thethermoplastics used in commercial paperboard polyfoil laminates have lowdielectric losses. This makes it difficult to induce a current andrequires excessive power to generate strong electromagnetic fields orlong exposure periods to adequately heat the thermoplastic layer.

A third technique of heating is by induction; subjecting the compressedpolyfoil laminates to an alternating electromagnetic field having afrequency in a range from about 5 KHz to 2 MHz, to induce an eddycurrent in the area of the metallic foil layers subject to theelectromagnetic field. These induced currents generate heat in the foilbecause of resistance losses and the heat softens the adjacentthermoplastic layers by conduction. Examples of induction heatingtypically place an induction coil, electrically connected to a highfrequency generator, adjacent the area where the current is to beinduced. Commercial high frequency generators have powers varying from afew watts to about 30 kw. In some examples, the current is induced in ametallic foil layer adjacent the thermoplastic material e.g., U.S. Pat.Nos. 4,248,653 to Gerger, 3,864,186 to Balla, 3,873,961 to Vouillemin,3,730,804 and 3,879,247 to Dickey, 3,723,212 to Casper, 3,556,887 toAdcock et al., and 3,424,885 to Garney et al. In other examples thecurrent is induced in other conductive materials, such as finely dividedcarbon particles or iron oxide applied to or sandwiched betweenthermoplastic materials, e.g., U.S. Pat. Nos. 4,264,688 to Balla,3,730,804 and 3,879,247 to Dickey, 3,652,361, 3,462,336 and 3,396,258 toLeatherman, 3,574,031 to Heller, 3,367,808 to Edwards and 3,450,856 toBuck.

The package forming machines using induction heating to form transverseseals presently available cannot be adapted to operate fast enough to beeconomical and competitive because the electromagnetic field isgenerated by an induction coil that is electrically and directlyconnected to the high frequency generator. Furthermore, induction coilsthat operate continuously, for lengthy periods of time must also have acooling means for preventing the coil from overheating, melting, andshorting the generator, e.g., a source of circulating water connected toand flowing through a hollow portion of the coil. The electrical andcooling connections restrict the movement of the induction coil. Thesemachines are primarily limited to intermittent sealing, where the coilonly moves toward and away from the polyfoil laminate, and slowreciprocation because the distance an induction coil can travel in thedirection of travel of the polyfoil is limited by the length of theelectrical and cooling connections, and the coil must return to thestarting point for each seal. Consequently, any continuous production ofsealed packages would be very slow, inefficient, and uneconomical.

Secondary induction coils generate electromagnetic fields by beingsubjected to a first electromagnetic field generated by a primary coilelectrically connected to the generator, having a current induced, andusing that inducted current to generate the second field. They are notdirectly connected to a high frequency generator. The problem with knownsecondary induction systems is that they were designed for soldering,brazing, or heat treating small parts such as capacitors or resistors.These methods use plate conductors that are mounted on turntables ortranslating frames to move the coil in and out of the primary coil'selectromagnetic field. The known methods do not have the rigidnessrequired to simultaneously exert pressure on and inductively heat theworkpiece in cooperation with a pressing surface, nor the speed orcontrol necessary to seal commercially available polyfoil materials.Furthermore, these secondary induction coils could never be used tocompress the workpiece because of the severe damage that would result,e.g., shorting the generator, burning out the coil.

SUMMARY OF THE INVENTION

In order to overcome the problems inherent in traditional inductionsealing techniques, and in particular to increase the production rate ofsealed packages, secondary induction coils are used within a rigid jawcompressing a polyfoil tube filled with a product, to induce a currentin the polyfoil and seal the tube transversely.

A plurality of secondary induction coils, electrically insulated fromone another, from the primary induction coil connected to the highfrequency generator, and from ground, are mounted on an endless carryingmeans arranged so that each secondary induction coil will be passedthrough the electromagnetic field generated by the primary inducioncoil. Preferably the carrying means is a belt-like carrying meansinterposed between the primary induction coil and a traveling web ofpolyfoil materials. The traveling web may comprise two webs arranged sothat two thermoplastic materials are opposing and superimposed, or itmay comprise one web that has been folded and sealed longitudinally toform a tube having the thermoplastic as the inner surface.

The carrying means advances at the same speed as the polyfoil materialand has one path segment ("Path A") where the movement of the carryingmeans is parallel to the traveling foil. The second induction coils,moving as part of the belt-like carrying means, advance at the samerate. The advance is preferably continuous. When moving along Path A,the secondary induction coil passes through the electromagnetic fieldgenerated by the primary induction coil, close to the surface of theprimary induction coil.

Each secondary induction coil is mounted as a part of a nonconductiverigid sealing jaw. Each sealing jaw is mounted on the carrying means andhas an opposing corresponding rigid pressure jaw mounted on a carryingmeans so that, as the carrying means advance, each sealing jaw andcorresponding pressure jaw contact and compress the polyfoil tube.Preferably the pressure and sealing jaws are arranged on an endlessbelt-like carrying means so that both carrying means rotate continouslyin opposite directions and the sealing and pressure jaws move in thesame direction while in Path A. In this path segment, the sealing jawand pressure jaw contact and compress two portions of the polyfoiltransversely from opposite sides of the polyfoil tube, expressing anyproduct, so that the two thermoplastic materials are in contact andthere is no relative movement between the sealing jaw, the pressure jaw,and the polyfoil material as they advance.

As each secondary coil passes through the electromagnetic field, one byone, an induced current flows in the area of the secondary inductioncoil subjected to the electromagnetic field. The secondary inductioncoil is designed to be responsive to the electromagnetic field generatedby the primary induction coil. For example, when the electromagneticfield is generated by a pancake coil, the secondary induction coil maybe an elongated twin loop folded over on itself to have a U-shape,longer than it is wide, so that one loop is fully subjected to theelectromagnetic field.

The current induced in the secondary induction coil passes through allparts of the coil and consequently generates and radiates a secondelectromagnetic field. The second electromagnetic field would thus begenerated by the induced current flowing through the other loop of thetwin loop secondary induction coil.

The second electromagnetic field induces a second current in the area ofthe metallic foil layer contacted and compressed by the sealing jaw,proximate to the secondary induction coil located in the sealing jaw andthus subject to the second electromagnetic field. The second inducedcurrent causes the foil to heat because of resistance losses, and theheat will soften the adjacent thermoplastic materials. Because they arepressed together, the two thermoplastic layers will fuse.

When the secondary induction jaw is no longer subjected to theelectromagnetic field generated by the primary induction coil, nocurrent is induced, no second electromagnetic field is generated, and noheat is generated. This occurs when the carrying means advance and movethe sealing jaw away from the surface of the induction coil. The fusedthermoplastic material will then cool, harden, and form a seal. Thesealing jaw and pressure jaw maintain the polyfoil materials pressedlightly together until the thermoplastic material has hardened. Thus, atthe end of Path A, the pressure jaw and sealing jaw release the sealedpolyfoil material as the carrying means advance to bring the jaws backto the beginning of Path A.

The preferred practice includes severing the seals after thethermoplastic materials have hardened with a knife mounted in thepressure jaw. The knife perforates the polyfoil in the sealed area andpasses through a corresponding gap in the sealing jaw to sever polyfoil.

It is also preferred to have an alignment means for aligning the sealingjaw and the pressure jaw as they contact and compress the polyfoil. Suchan alignment means may comprise a pair of ball studs mounted in thesealing jaw and a corresponding pair of sleeves mounted in the pressurejaw. The ball studs are received inside the sleeves when the polyfoil iscompressed between the sealing jaw and pressure jaws, near the beginningof Path A. The alignment means thus prevents any twisting of the sealingand pressure jaws relative to each other when clamped about thepolyfoil.

It is also preferred to utilize a means for preforming the tube at alocation below where the seal wil be made and above where the precedingseal was made, preferably at about the midpoint of the package to beformed, and will occur before the pair of corresponding sealing andpressure jaws that will form the seal to be made contact and compressthe polyfoil tube. The preforming step involves pressing in the edges ofthe polyfoil material about to be sealed to increase the volume enclosedby the material so that the tube is relatively more fully filled beforethe package is sealed. A second preforming means for preforming thepackage by prebreaking the scored and creased polyfoil tube may beprovided at a location above the first preforming means to assist thefirst preforming means providing a more uniform fill.

It is therefore an object of this invention to provide a method andapparatus for sealing polyfoil materials together by induction, using asecond induction coil not directly connected to a high frequencygenerator to receive electromagnetic energy and to generate anelectromagnetic field on the area of the polyfoil to be sealed.

It is another object of this invention to provide a method and apparatusfor sealing polyfoil laminate webs continuously, at a high rate of sealsper minute.

It is another object of the invention to seal metallic foil andthermoplastic laminates by use of high frequency generators withoutrequiring direct connection between the induction coil that induces thecurrent in the metallic foil and the generator while the laminates aretightly pressed together and advancing continuously, and the secondaryinduction coils are advancing at the same speed as the laminate.

It is another object of this invention to provide a plurality ofsecondary induction sealing jaws and pressure jaws spaced apart forgripping two opposing sides of polyfoil material sequentially, one setof sealing and pressure jaws after another, preforming the polyfoil tubeto expand the volume of the tube to be sealed, forming discrete sealedcontainers from a continuously forming and advancing tube of polyfoilmaterial being filled with a product, inductively sealing the tubetransversely, relative to the direction of travel of the tube, andsevering the seals to make sealed containers, particularly asepticsealed containers, at a high rate of speed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 illustrates a schematic perspective view of the continuousinduction sealing apparatus in accordance with the present invention.

FIG. 2 illustrates a schematic front section view of the continuousinduction sealing apparatus in accordance with the present invention.

FIG. 3 is a sectional front view of FIG. 1.

FIG. 4 is a sectional face view of the primary induction coil of FIG. 1.

FIG. 5 is a top sectional view of FIG. 4 taken along lines 5--5.

FIG. 6 is a partial top section view of FIG. 3 taken along line 6--6.

FIG. 7 is a partial front view of FIG. 1 taken along line 7--7.

FIG. 8 is a top section view of FIG. 7 taken along line 8--8.

FIG. 9 is a perspective view of a secondary induction coil-sealing jawand a pressure jaw in accordance with an embodiment of the presentinvention.

FIG. 10 is a rear view of the secondary induction coil of FIG. 9.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIG. 1, an illustrative embodiment of this invention isuseful in connection with machines 10 that form polyfoil tube 80 frompolyfoil web 82, fills polyfoil tube 80 with product 84, preforms andseals polyfoil tube 80 transversely, and severs the seal to formdiscrete packages 210 containing relatively uniform amounts of product84. The method of folding, filling, and vertically sealing web 82 toform filled tube 80 is known in the art.

As shown in FIGS. 1 and 2, an illustrative embodiment of the apparatusof this invention comprises high frequency generator 16, primaryinduction coil 20, .[.pluraity.]. .Iadd.plurality .Iaddend.of secondaryinduction coils 32, plurality of sealing jaws 30, first endless carryingmeans 50, plurality of pressure jaws 60, second endless carrying means70, top preforming wheels 12a and 12b, and bottom preforming wheels 13aand 13b. Sealing .[.3aws.]. .Iadd.jaws .Iaddend.30 are nonconductive andmounted on and spaced along first carrying means 50. Secondary inductioncoils 32 are mounted in sealing jaws 30. Pressure jaws 60 are mounted onand spaced along second endless carrying means 70.

Top preform wheels 12a and 12b having plurality of spokes 14a and 14brespectively, oppose each other and are mounted on opposite sides oftubes 80 so that one of spokes 14a of wheel 12a and one of opposingspoke 14b of wheel 12b contact the sides of tube 80 and press theopposing sides inwardly so that the tube 80 will expand and fill withproduct 84. If tube 80 has previously been scored and creased by meansknown to those in the art, then pressing the edges of tube 80 may alsobegin to form package 210 along the predetermined scored fold lines. Thepreform wheels also provide for proper registration of the printedmatter on a formed package when the polyfoil is preprinted for packagelabeling. If the tube is not preformed, the corresponding sealing andpressure jaws might not grab polyfoil tube 80 at the place where theprint for two adjacent packages meet. Thus part of the print for twopackages may appear on the same package. Preforming can adjust thelength of tube 80 so that the jaws can grab polyfoil tube 80 at theproper location, assisting in the print registration so that the printfor a package is properly arranged on that package.

Preform wheels 12a and 12b are constructed and driven synchronously sothat spokes 14a' and 14b' contact tube 80 at a location on the tube atabout the same time. The location on tube 80 is preferably about themidpoint of the portion of tube 80 corresponding to a package, beforetube 80 is contacted by sealing jaw 30 and pressure jaw 60. The speed atwhich preform wheels 12a and 12b rotate is adjusted to correspond to thespeed of tube 80 so that one pair of spokes will preform tube 80 foreach package to be made and there is minimal vertical relative movementbetween the end of the spokes and tube 80 during preforming.

Bottom preform wheels 13a and 13b, having respective plurality of spokes15a and 15b, are similar to wheels 12a and 12b in construction,function, and alignment. Bottom preform wheels 13a and 13b are arrangedin opposition and may be spaced below top wheels 12a and 12b preferablyby about the length of two packages. Therefore, in the preferredembodiment each package formed will have been preformed by both toppreform wheels 12a and 12b and bottom preform wheels 13a and 13b beforebeing sealed transversely. In an alternate embodiment, only bottompreform wheels are used. In yet another embodiment, no preform wheelsmay be required depending on the operating speed and the nature of thepolyfoil used, the size of the package, and the filling material.

First and second endless carrying means 50, 70 are arranged and drivensynchronously so that in a part of their paths, Path A, first and secondcarrying means are in opposition on opposite sides of polyfoil tube 80,and are rotating in a plane perpendicular to the plane formed by top andbottom preform wheels 12a, 12b, 13a and 13b. As a section of polyfoiltube passes through the apparatus, top preform wheels 12a and 12bcontact and preform tube 80, bottom preform wheels 13a and 13b contactand preform tube 80, each seal jaw 30 opposed a corresponding pressurejaw 60, transversely contacting and compressing between them preformedand filled polyfoil tube 80 so that the inner thermoplastic material istightly pressed together. Sealing jaw 30, pressure jaw 60, and polyfoiltube 80 advance simultaneously at speed V, so that sealing jaw 30 passesand is subjected to the first electromagnetic field generated by primaryinduction coil 20, generates a second electromagnetic field, andsubjects the metallic foil material of polyfoil tube 80 to the secondelectromagnetic field. This induces a current in the metallic foil,heating and softening and fusing together the pressed thermoplasticmaterial. When sealing jaw 30 passes beyond and is no longer subject tothe first electromagnetic field, no currents are induced in thethermoplastic material or secondary induction coil 32 and no heat isgenerated. The thermoplastic material then cools and hardens, forming atransverse seal. The longer the time period the heated polyfoil tube ispermitted to cool while compressed between the sealing and pressure jaw,the more likely it is that the resulting seal will be hermetic. The morepairs of corresponding sealing and heating jaws the more packages havinghermetic seals, or aseptic packages, can be made. Thus it can be seenhow packages having transverse seals made in accordance with thisinvention can be produced in large quantities and at cost savings bycontinuously sealing at a high rate of speed.

For simplicity, the drawings will be described in connection with onlyone set of corresponding sealing jaw 30 and pressure jaw 60 as theyproceed along Path A. It is to be understood however, that there may bemore than one set of corresponding sealing jaw and pressure jaw,continuously advancing through each stage of the sealing operation,producing a plurality of transverse seals spaced apart along polyfoiltube 80.

FIG. 2 shows how primary induction coil 20 is electricaly connected tohigh frequency generator 16 by a pair of electrically conductive busbars18. Busbars 18 typically are a solid conductor, e.g., copper oraluminum, and may be rigid or flexible. Alternately, the pair of busbarsmay be replaced with a coaxial cable to maximize the power transfer fromthe generator to the primary coil. High frequency generator .[.18.]..Iadd.16 .Iaddend.is a commercially available induction frequencygenerator that can generate frequencies up to 450 KHz at about 5kilowatts, e.g., 5 kw Lepel generator, model No. T53DFSW, type T50653,as may be purchased from Lepel Industries, New York, N.Y.

FIGS. 4 and 5 show the construction of primary induction coil 20.Electrically conductive tubing 22, typically substantially of copper, iswound spirally into pancake coil 24. FIG. 5 shows how tubing 22 ishollow so that a source of water (not shown) can flow continuouslythrough tubing 22 to absorb heat generated by resistance losses and thuscool pancake coil 24 during operation. Water cooling is common in theinduction art. Tubing 22 is electrically connected in a conventionalfashion to busbar 18 (not shown), completing the circuit, so thatcurrent will cycle through generator 16, busbars 18, and pancake coil24. As current passes through tubing 22, a dynamic electromagnetic fieldis generated by pancake coil 24. The electromagnetic field is composedof an electronic field component, radiating outwardly from the surfaceof pancake coil 24, and a magnetic field component, radiating radiallyalong the surface of coil 24. The strength of the fields decreasessignificantly with increasing distance from the surface. The effectiveelectromagnetic field is substantially the magnetic field componentlocated adjacent and in close proximity to the surface area of primaryinduction coil 20. The range of the effective electromagnetic fielddepends upon the power of generator 16 and the configuration of pancakecoil 24. Pancake coil 24 is mounted on bulkhead 26, a materialcomprising Celcoa 2500 as available from Celanese Corporation, CelaneseEngineering Resins, Chatham, N.J., having a high dielectric value of1200 v/mil to insulate the first electromagnetic field from ground.Primary induction coil 20 also has cover 28 secured over the frontsurface area of pancake coil 24, for protecting the coil, preventingelectrical shorts, and securing the coil rigidly in its pancake, spiralorientation.

FIGS. 1, 2, and 3 show how primary induction coil 20 is mounted relativeto first endless carrying means so that sealing jaw 30 and pressure jaw60 are opposing and contact and compress polyfoil tube 80 before sealingjaw 30 enters and is subject to the effective electromagnetic fieldgenerated by primary induction coil 20. As sealing jaw 30 enters andpasses through the effective electromagnetic field, it acts as asignificant load on primary induction coil 20 and generator 16, and acurrent is induced in secondary induction coil 32 of sealing jaw 30having the same frequency as the current in primary induction coil 20.

FIG. 6 shows the orientation of sealing jaw 30 relative to primaryinduction coil 20 when sealing jaw 30 is located in the effectiveelectromagnetic field. Gap 200 between cover 28 and sealing jaw 30 isintended to be as small as possible. In practice, the size of the gapdepends upon how efficiently the system is to be operated, how muchvibration exists when carrying means 50 and 70 are advancing, how closemachinery tolerances can be maintained, and the power of high frequencygenerator 16. A gap of about 0.063" has been used satisfactorily.

As shown in FIGS. 6, 7, 8, and 9, each sealing jaw 30 compriseselectrically conductive secondary induction coil 32, typically 99% purecopper having thin loop 36 and thick loop 38, base 34, end portions 40,and brackets 42 for mounting sealing jaw 30 on endless carrying means50.

Base 34 and end portions 40 are electrically nonconductive materialsthat isolate secondary .Iadd.induction .Iaddend.coil 32 from ground yetare capable of withstanding the pressures required to compress, seal,and sever polyfoil tube 80. A typical material is G-10 or G-11 epoxy andfiberglass resin, commercially available from Synthane-Taylor, ALCOStandard Company, Valley Forge, Pa.

Base 34 is adapted to receive coil 32 so that thin loop 36 is transverseto polyfoil tubing 80. Base 34 and end portions 40 have beveled faces 48and 49, creating a trapezoidal-like cross section as shown in FIG. 7.The trapezoidal cross section permits sealing jaw 30 to engage andcompress polyfoil tube 80 at sealing pressing surface 41 withoutentrapping any significant amount of product 84, as sealing jaw 30 isbrought by B at the top of Path A and in contact with polyfoil tube 80by first carrying means 50, as shown in FIG. 1.

Thin loop 36 is one piece of conductive material having thin gap 37extending along most of its longitudinal midline. Thin loop 36 and thingap 37 of this embodiment have been designed to have a plate-likeconfiguration transverse to the direction of advance of polyfoil tube80, thin gap 37 being longer than flattened tube 80 is wide to ensure auniform transverse seal, and wide enough to receive a blade for severingthe transverse seal. The face of thin loop 36 forms part of sealingpressing surface 41 and must be wide enough to conduct current atsufficient intensity to induce a current in the metallic layer ofpolyfoil tube 80 that will heat, and soften, and fuse the opposingthermoplastic layers of polyfoil tube 80 pressed transversely betweensealing jaw 30 and pressure jaw 60, to form the seal. Similarly, theseal must be wide enough to retain its integrity after it is severed.

Thick loop 38 is designed to respond to the nature and orientation ofthe effective electromagnetic field generated by primary induction coil20 to have a current induced in it as sealing jaw 30 traverses theeffective electromagnetic field. Because secondary induction coil 32 isone piece, the induced current will be the same in both thick and thinloops 36, 38, and must be adequate to form the seal in polyfoil tube 80as described above. .[.The action is such that a first current isinduced in loop 38 by the primary field of coil 20, a second current isinduced in loop 36, and a third current is induced in the electricallyconductive layer of the packaging material..].

In the preferred embodiment, as shown in FIGS. 6 and 7, thick loop 38resembles a thick, rectangular plate having oval 39 cut out of thecenter, and a slit extending longitudinally from the oval to one edge toform a single turn loop (see FIG. 10). The dimensions shown in FIGS. 6,7, and 10 are representative of the functional, relative dimensions. Forexample, oval 39 is about 1.5 inches by 0.75 inches and the slit isabout 0.015 inches. Preferred secondary induction coil 32 is oneinduction coil having two U-shaped loops of different configuration, theloops being about the same length arranged essentially in parallel andsuperimposed planes, connected together at the end having the slitscorresponding to the open end of the U-shape. Secondary induction coil32 is secured to base 34 by brass screws 44.

Thin loop 36, having the same current that is induced in thick loop 38,generates a second electromagnetic field, different from and moreconcentrated than that generated by primary induction coil 20. Thesecond electromagnetic field has an electrical field component directedoutwardly along the length of thin loop 36 and a magnetic fieldcomponent perpendicular to and along the length of thin loop 36. Themagnetic field consequently induces a current in the area of themetallic layer of polyfoil tube 80 parallel to the length of thin loop36.

End portions 40 are secured to .[.ends 46 and 47 of.]. base 34 by screws45. Brackets 42 are attached to end portions 40 by brass screws 43 formounting sealing jaw 30 to first carrying means 50.

As shown in FIGS. 6, 7, 8, and 9, pressure jaw 60 comprises base 62,slot 64, knife 66, grooves 68, cushioning means 72, end pieces 74,brackets 76, and piston receptacles 78. Base 62 need not be electricallynonconductive, although it is preferred that base 62 be a material thatis not readily susceptible to induction heating so that it will not actas a load on high frequency generator 16, e.g., stainless steel.Pressure jaw end portions 74 are made of an electrically nonconductivematerial e.g., G-10 or G-11, so that each pressure jaw 60 iselectrically isolated from ground. Slot 64 extends longitudinally alongand through pressure jaw 60 and is adapted to receive and pass knife 66.Knife 66 is used to perforate and sever sealed polyfoil tube 80 afterthe seal has formed. Grooves 68 extend longitudinally along the front ofpressure jaw 60, one on either side of slot 64, and are adapted toreceive cushioning means 72, a resilient nonstick material, e.g.,rubber. Cushioning means 72 is pressed against polyfoil tube 80 tocontact and compress but not stick to polyfoil tube 80 during and afterforming and severing of the seal. Pressure jaw 60 and end portions 74have beveled faces 48, 49, giving jaw 60 a trapezoidal-like crosssection that is generally the mirror image of the cross section ofsealing jaw 30, as both are shown in FIG. 7. This configuration permitspressure jaw 60 to contact and compress polyfoil tube 80 withoutentrapping any significant amount of product 84 between pressure jaw 60and similarly contacting and compressing sealing jaw 30.

Attached to the rear of base 62 are a pair of piston receptacles 78, asshown in FIG. 6, each being adapted for receiving knife pushrodmechanism 86 for actuating knife 66. Knife pushrod mechanism 86comprises cylinder 98, cylinder bearing 96 inserted within cylinder 98,preferably of a teflon-like material, pushrod 88 secured at one end toknife 66 having a first diameter and at the other end being attached tocylinder head 92 having a second diameter larger than the firstdiameter, adapted to slide smoothly in contact with cylinder bearing 96,and spring 90 secured about pushrod 88 and between the back of pressurejaw base 62 and cylinder head 92. Wheel 100 is pivotably mounted in theend of cylinder head 92 and is responsive to cam 102.

A pair of cams 102 are located on base 12 of machine 10, at the lowerpart of Path A. They are mounted in parallel horizontally, and in linewith the path of wheels 100 so that as pressure jaw 60 moves downwardly,wheels 10 contact cams 102 at a location below where the seal hasformed, and cams 102 cause knife pushrod mechanism 86 to translate,forcing knife 66 to contact, perforate, and sever polyfoil tube 80.Springs 90 maintain pushrod mechanisms .[.82.]. .Iadd.86 .Iaddend.biasedagainst cams 102 so that when cams 102 cease to exert a pushing force onpushrod mechanism 86, pushrod mechanism 86 will retract knife 66 withinpressure jaw 60, while sealing Jaw 30 and pressure jaw 60 maintainpolyfoil tube 80 compressed.

Knife 66, knife pushrod mechanism 86, piston receptacles 78 and cams 102are optional elements that facilitate handling of packages produced inlarge quantities at high rates of speed.

As shown in FIGS. 6 and 9, in the preferred embodiment sealing jaw 30has ball studs 110 mounted in end portions 40, and pressure jaw 60 hascorresponding sleeves 112 inserted into holes drilled in end portions74. When sealing jaw 30 and pressure jaw 60 are brought in opposition atB, as shown in FIG. 1, ball studs 110 will enter and be retained insleeves 112 so that thin gap 37 will align properly with correspondingslot 64 and knife 66 can extend from slot 64 into thin gap 37 withoutcontacting any part of thin loop 36 or base 34. The ball stud and sleeveconstruction permits sealing jaw 30 and pressure jaw 60 to move towardsand away from each other and to pivot into and out of opposition butwill not permit them to twist relative to each other. This also providesthat seal pressing surface 41 will squarely oppose resilient means 72and form a uniform seal in polyfoil tube 80.

As shown in FIGS. 3, 7, and 8, endless carrrying means 50 and 60 aremirror images of each other and will therefore be discussed with regardto only one. Each endless carrying means comprises two movable endlesschains 124 that are joined together when the sealing or pressure jawsare connected. Each chain 124 comprises a plurality of brackets.[.114.]. .Iadd.42 or 76.Iaddend., plurality of wheels 116, plurality offill plates 120, and volume control tracks .[.122.]. .Iadd.124.Iaddend..Each chain 124 is mounted on a pair of sprockets 14, arranged atopposite ends of Path A, having drive means 118 connected to eachsprocket 14 for rotating the sprocket and thus controlling the speed andtension of chains 124 to correspond to speed V of polyfoil tube 80.

Referring to FIGS. 7 and 8, it is seen how two wheels 116 are pivotallymounted to the lower end of bracket .[.114.]. .Iadd.42 or 76.Iaddend..Wheels 116 are adapted for retention in sprockets 14, for moving in andout of segment A, and for rolling along volume control tracks 122. Theupper end of bracket .[.114.]. .Iadd.42 or 76 .Iaddend.is secured toeither sealing jaw 30, pressure jaw 60, or a fill plate 120. Fill plates120 are designed to provide a flat surface for preventing bulges inpolyfoil tube 80 during the compressing and sealing operation and arealternated between jaws so that fill plate 120 on first carrying means50 opposes fill plate 120 on second endless carrying means 70..[.Preferably brackets 114 are the same as brackets 42 when used tosecure sealing jaws 30 to first carrying means 50, and brackets 114 arethe same as brackets 76 when used to secure pressure jaws to secondcarrying means 70..].

FIG. 3 shows how each wheel 116 is connected to two brackets .[.114.].,42, or 76, thereby forming endless carrying means 50 and 70. Volumecontrol tracks 122 are mounted on base 12 and are adjustable to controlthe distance between sealing jaws 30 and pressure jaws 60 and opposingfill plates 120, thereby supporting polyfoil tube 80 as product 84 isinserted into polyfoil tube 80 through filler tube 104, in accordancewith the designed volume desired and dimensions of the tube. The meansfor adjusting the volume do not form a part of this invention.

Volume control tracks 122 also provide a support for wheels 116 so thatsealing jaw 30 will not move away from polyfoil tube 80 when pressurejaw 60 is urged against polyfoil tube 80 and vice versa. In a preferredembodiment, volume control tracks 123 support pressure jaws 60 and haveraised portion C that urges pressure jaw 60 towards sealing jaw 30 totightly press polyfoil tube 80 transversely, so that product 84 is morefully expressed from between the two thermoplastic material layers to besealed together.

Means for conveying severed packages may be provided as shown in FIGS. 1and 2. Further means for forming the severed packages into desiredshapes, for example, bricks, may also be provided (not shown). Neitherof these means form a part of the invention.

The method and apparatus of sealing polyfoil tube 80 in accordance withthe invention is described above, and below, in connection with thefollowing example.

EXAMPLE

A test was performed using the apparatus substantially as describedabove. The high frequency generator was a 5KW Lepel generator. Thepolyfoil material used was manufactured by International Paper Company,New York, N.Y. The polyfoil was about 0.9 micrometers thick, andcomprised the following layers with their respective density (whereavailable): external layer of polyethylene (15 g/m²); a layer of paper(200±35 g/m²), a junction layer of polyethylene (20 g/m²); a layer ofaluminum foil; and an internal layer of polyethylene (55±5 g/m²). Themetallic foil layer was about 0.00035" thick. The web was originally 12"wide and after being folded in half was just less than 6" wide.

The primary induction coil, about 6.5 inches in diameter, was connectedto the generator output by a coaxial cable, and connected to a watersupply which provided water circulating through the hollow coppertubing. The sealing jaws, substantially as described above, were mountedon endless carrying chains that were mounted on sprockets driven by amicroprocessor controlled drive mechanism for providing uniform speedcontrol relative to the web speed.

The microprocessor also controlled the drive means for the top andbottom preforming wheels so that packages could be properly created atany selected speed. Furthermore, the microprocessor was used to adjustthe power output of the high frequency generator to coincide with thespeed at which the tube was advancing so that the secondary coil willreceive enough energy to induce a large enough current for a timeadequate to melt the thermoplastic layer of the polyfoil and form ahermetic seal. The speed and power relationship was predetermined bytrial and error bench tests that established the correlation. Therelationship was then used by the microprocessor which adjusted thegenerator power in response to the tube speed.

The secondary coil dimensions were based on the desire to minimize thegenerator power used by maximizing the current distribution and flow inthe coil, without detracting from the structural integrity of the coil.The dimensions also control the secondary electromagnetic fieldgenerated by the coil because of the current distribution in the coil.It was determined that the preferred ratio of the surface area of theloop to the cross sectional area of the loop was about 3.9 for each ofthe thin loop and the thick loop. A ratio of 4 to 1 was examined but thethin loop would not be thick enough to carry the current withoutrequiring some additional menas for cooling the secondary coil.

The secondary induction coil was about 7" long. The thin loop was about0.25" wide and 0.152" thick, the thin gap about 0.125" wide, and thesealing pressing surface was about 0.43" wide. The thick loop was about1.0" wide and .Badd..[.187.]. .Baddend..Iadd.0.187.Iaddend." thick andhad a concentric oval aperture about 1.5" by 0.75" arranged so that thelong axis was parallel to the length and the short axis wasperpendicular. A thin slit about 0.015" wide extended from one end ofthe coil to the oval, forming the rectangular plate-like structure intoa single loop about 2" wide. (See FIG. 10.) The distance between the twoloops was about 0.631" and two tapered pieces of conductor connected thethick and thin loops together at the ends of the loops having the slitsso that the induced current would flow through both loops of thesecondary coil. The center distance between adjacent sealing jaws (andpressure jaws) was 4.187 inches.

The plurality of sealing jaws and pressure jaws were advanced, with thesealing jaws passing the primary induction coil, one after the other,downwardly, about 0.063 inches from the front surface of the primarycoil. The pressure jaws then passed the cams activating the knife tosever the filled and sealed containers. Both jaws then returned to thetop to form another seal, as shown in FIGS. 1 and 2.

A conventional double unwind stand and butt splicer, type SHD-800ABR-EG,purchased from Compensating Tension Controls, Inc., West Caldwell, N.J.,contained two rolls of polyfoil web. The web was guided over guiderollers that maintained the web in tension and folded the web in half sothat the thermoplastic material layer was on the inside. A filler tubewas placed into the folded section and the longitudinal sealing meanssealed the overlapping edge of the web continuously as the web advanced,thus forming the polyfoil tube.

The web guiding, folding, longitudinal sealing, and filling do not forma part of this invention. However, the longitudinal seal means includedan induction coil for heating the longitudinal seal area by induction.Pressure to form the seal was provided by separate pressing means. Theinduction coil was connected to a Linberg/Cycledyne 3 KW high frequencyinduction generator having a nominal frequency of 450 KHz and operatedat about 30-35% power. The generator is commercialy available fromLinberg/Cycledyne Company, Chicago, Ill.

Web speed used in the test runs was about 46.5 feet per minute. Thisspeed produced 125 packages per minute and each package contained about250 ml of fluid.

The filling section filled the tube with water, and maintained the waterlevel within a range that could accommodate the repeated compression ofthe polyfoil tube as it was formed and new seals were being made withoutrising to the longitudinal seal area.

The top and bottom preforming wheels were aligned on opposite sides ofthe advancing tube and rotated at a speed so that a spoke would contactthe tube and expand the volume to more fully fill the tube with water.

The sealing jaws and pressure jaws were aligned in opposition to contactthe polyfoil tube filled with water, using ball studs mounted in thesealing jaw entering the sleeves inserted in the pressure jaw to ensurealignment.

From prior experiments it has been learned that in the absence of thealignment means, some of the sealing jaws could be damaged by thesevering action the knife. While the damage did not necessarily relateto imperfect seals, adding the alignment means significantly reduced thelikelihood of damage to the secondary induction coil, and prolonged thelife of the machine.

The sealing jaw and pressure jaw pressed the sides of the preformedpolyfoil tube inwardly, displacing the water level upwardly and ensuringthat the envelope below the sealing jaw was completely filled withwater. The opposing jaws moved downwardly at a rate of 46.5 feet perminute, equal to the speed of the polyfoil tube. After an initialcompression, the pressure jaw was urged towards the sealing jaw to morecompletely express the water from the seal area, and to press thethermoplastic material layers, transversely flat against each other. Apressure of 45 psi was used. It was found that lower pressure could beused, especially at slower speeds of web advance, to provide regularcomplete seals, but leaks might form and the forces required by theknife to sever the sealed packages (about 60 psi) could break or weakenthe seal.

The strength of the electromagnetic field is dependent upon the outputof the generator. The 5 KW Lepel high frequency generator parameterswere as follows: power setting at 60%, KC (grid modulating frequency) at90, grid current of 0.4 Amps-DC, plate current of 1.15 Amps-DC, and Tap(impedance matching of primary coil) at 15. The distance between thesealing jaw and the primary coil was 0.063 inches. The sealing jaw took2.86 seconds to pass by the primary induction coil, traveling a distanceof 6.5 inches. During that time, a first current of unknown magnitudewas induced in the secondary induction coil and a second current ofunknown magnitude was induced in at least one of the metallic foillayers of the polyfoil tube, heating the metallic foil by resistancelosses and the adjacent facing thermoplastic layers by conduction, sothat the facing thermoplastic layers softened and fused into one mass.The actual frequency produced by the primary coil was about 425 KHz.

Once having passed beyond the primary induction coil, no significantcurrent was induced in either the secondary induction coil or themetallic foil layer. This permited the fused thermoplastic to solidifyand form a hermetic seal while pressed between the jaws. Two seals wereformed, each about 0.25" wide, with a gap inbetween wide enough to besevered by the knife without breaching either of the seals. The twoseals generally corresponded to the surface area of the thin loop of thesecondary induction coil in the pressing surface. Bench tests haddetermined that if a slower tube speed or greater generator power hadbeen used, the seal area might have comprised one seal rather than twodiscrete seals.

This test ran for 30 minutes without any significant failure intransverse seals. During this time, the secondary induction coilsreached a steady state temperature of 140° F.

We claim:
 1. A method of sealing packaging material having a layer ofthermoplastic material and a layer of electrically conductive materialcomprising:(a) compressing the packaging material together between firstand second rigid members so that a first thermoplastic material portionis pressed against a second thermoplastic material portion with norelative motion between the first and second rigid members and the firstand second thermoplastic material portions, the first and second rigidmembers being electrically isolated from ground and the first rigidmember having an electrically conductive material on its surface.[.which contacts the packaging material and which is in the form of afirst loop and also having a second electrically conductive material inthe form of a second loop, said first and second loops being separatedby a rigid, nonconductive material.].; (b) generating a .[.primary.]..Iadd.first .Iaddend.electromagnetic field having an effective range forinducing a current in an electrically conductive material brought withinthe effective range; (c) inducing from said .[.primary.]. .Iadd.first.Iaddend.electromagnetic field a first current in the .[.second.].electrically conductive material .[.loop.]. of the first rigid member bymoving the first rigid member into the effective range of said.[.primary.]. .Iadd.first .Iaddend.electromagnetic field therebygenerating a second electromagnetic field from the first current flowingin the .[.second.]. electrically conductive .[.loop.]. .Iadd.material.Iaddend.of the first rigid member.[.,.]. .Iadd.; .Iaddend. (d) inducingfrom the second electromagnetic field of the .[.second loop.]..Iadd.electrically conductive material of the first rigid member.Iaddend.a second current in the .[.first loop thereby generating athird electromagnetic field.]. .Iadd.electrically conductive materiallayer of said packaging material portion.Iaddend.; (e) fusing the firstand second thermoplastic material portions together by inducing from the.[.third.]. .Iadd.second .Iaddend.electromagnetic field .[.of the firstloop a third.]. .Iadd.said second .Iaddend.current in said electricallyconductive material layer of the packaging material for a period of timesufficient to generate enough heat as a result of the induced currentflow to soften and fuse together the first and second thermoplasticmaterial portions without adversely affecting the packaging materialand; (f) solidifying the heated thermoplastic material into an effectiveseal after it fused together by removing the first rigid member from theeffective range of the first electromagnetic field so that nosignificant induced currents flow, no heat is generated, and thethermoplastic material is allowed to cool and harden.
 2. The method ofclaim 1, further comprising:advancing the first and second rigid membersand the packaging material continuously, at the same rate of speed, sothat the first rigid member passes through the effective range of thefirst electromagnetic field while the packaging material is compressedbetween the first and second rigid members; and adjusting the speed atwhich the first and second rigid members and packaging material move andadjusting the strength of the first electromagnetic field so that thefirst rigid member is within the effective range of the firstelectromagnetic field for a period of time long enough to soften andfuse the facing thermoplastic materials without adversely affecting thepackaging material.
 3. The method of claim 2, furthercomprising:preforming the packaging material before the packagingmaterial is compressed between the first and second rigid members sothat the volume formed by the packaging materials is increased.
 4. Themethod of claim 2 further comprising;securing the first rigid means to afirst endless carrying means and securing the second rigid means to asecond endless carrying means; driving the first and second endlesscarrying means synchronously so that during each revolution the firstand second rigid members contact and compress between them the portionsof the packaging materials to be sealed together before the first memberpasses through the effective range of the first electromagnetic field;and releasing the sealed packaging materials after the thermoplasticmaterial has cooled and hardened.
 5. The method of claim 4 furthercomprising:securing a plurality of first rigid means to and spaced apartalong a first endless carrying means and securing a plurality of secondrigid means to and spaced apart along a second endless carrying means,so that each first rigid member has a corresponding second rigid member,and each adjacent set of first and second rigid members contact andcompress adjacent portions of packaging material to be sealedsequentially, along the length of the advancing packaging material. 6.The method of claim 5 further comprising:generating the firstelectromagnetic field by means of a primary induction coil locatedinterior to the first endless carrying means and electrically connectedto a high frequency induction generator.
 7. The method of claim 6further comprising:forming a tube continuously from an advancing web ofpackaging material by folding the packaging material so that thethermoplastic layer is folded on itself, inserting a product filler tubein the folded packaging material and sealing the folded packagingmaterial longitudinally, below where the filler tube is inserted;filling the tube of packaging material with a product as the tubeadvances; arranging the first and second endless carrying means oneither side of the advancing tube so that the first and second rigidmembers express the product from between the thermoplastic layers asthey contact and compress the sides of the packaging material tube. 8.The method of claim 7 further comprising:compressing the advancing tubeof packaging material with the first and second rigid members transverseto the direction of advance of the tube; and severing the packagingmaterial in the area sealed with a knife contained within the secondrigid means after the thermoplastic material has hardened but before thefirst and second rigid means release the packaging material so thatseparate packages are formed from the packaging material having sealstransversely to the tube and containing substantially uniform amounts ofproduct.
 9. The method of claim 8 further comprising:preforming theadvancing tube of packaging material by pressing the sides of the tubeinwardly with preforming means before the advancing tube is compressedtransversly so that the volume of the tube is increased and more productis introduced into the tube and enveloped in the package.
 10. The methodof claim 1 further comprising:aligning the first and second rigid meansby a ball stud attached to the first rigid member and a sleeve insertedin the second rigid member so that the ball stud enters and is retainedwithin the sleeve when the first and second rigid members have contactedand compressed the packaging material.